Pengfei Xia

Short Range Gigabit Wireless Communications Systems: Potentials, Challenges and Techniques

In this paper, we discuss multi-gigabits per second wireless networks in the 60GHz millimeter wave frequency band. Despite the large unlicensed bandwidth offered by the 60GHz frequency band, severe technical challenges exist towards making multi-Gbps a reality. We discuss the challenges in three different layers: PHY, MAC and the application layers. We also discuss some important technologies in overcoming these challenges, including antenna array beamforming, baseband modulation, data aggregation. The worldwide 60GHz regulatory and the ongoing standardization efforts are reviewed as well.

Multi-Stage Iterative Antenna Training for Millimeter Wave Communications

We study 60 GHz millimeter wave communication systems employing SVD based transmit precoding and receive combining, and propose a multi-stage iterative method in training the antenna coefficients. The antenna training is carried out in multiple stages one after another, while each stage features an iterative process based on the power iteration principle. Null space projection is used as an enabling step for iterative training in inner stages. The proposed training method is especially efficient for systems with a much smaller number of RF chains relative to the number of antennas on both transmitter and receiver sides.

A practical SDMA protocol for 60 GHz millimeter wave communications

We study spatial division multiple access in 60 GHz millimeter wave communications and focus on estimation of the optimal transmit beamforming vectors for stations and optimal receive beamforming vectors for the access point. An iterative antenna training protocol is developed, where the optimal transmit/ receive beamforming vectors are computed without explicit knowledge of the actual wireless channels. The proposed training method is especially attractive to systems with a much smaller number of RF chains relative to the number of antenna elements, thanks to its low training overhead.

Practical Antenna Training for Millimeter Wave MIMO Communication

We study antenna training method for millimeter wave MIMO communication systems and develop iterative antenna training (IAT) algorithm and protocols. The newly developed training method features low training overhead as well as low computation complexity, and has great application potential in practice.

Diversity Analysis of Transmit Beamforming and Its Application in IEEE 802.11n Systems

We study the diversity performance of multiple-input-multiple-output (MIMO) transmit beamforming when perfect channel state information is available at the transmitter side. In particular, we derive the achievable diversity order on each eigenmode in closed form. As an application, the diversity result is applied in average bit error rate (BER) approximation for IEEE 802.11n systems, where approximate BER performance bounds are obtained and further validated by numerical results.

DFT Structured Codebook Design with Finite Alphabet for High Speed Wireless Communication

A low-complexity numerical codebook construction method is presented in this paper for limited feedback transmit beamforming systems. The so-constructed codebook takes a DFT matrix structure and achieves equal amplitude beamforming all the time. The codebooks are designed such that the selected row indices mimic the behavior of a difference set which, when exists, is able to achieve codebook optimality. Finite alphabet constraint on the codebook is further studied, where scalar quantization is further applied.

WLC19-3: Analysis of Transmit Beamforming In IEEE 802.11N Systems

We study transmit beamforming in IEEE 802.11n systems, where perfect channel state information is available at the transmitter. We first derive the achievable diversity order on each eigenmode. It is found that these eigenmodes are almost Gamma distributed for small number of antennas, which is the typical configuration for IEEE 802.11n systems. Finally, we develop a tight lower- and upper-bound to the average bit error rate performance over each eigenmode.

Autonomous Coordinator Selection in Beamformed 60GHz Wireless Networks

In 60 GHz wireless networks, autonomous coordinator selection is required to find a device to coordinate the transmissions among devices. In order to minimize the power consumption for the coordinator, we utilize the direction information extracted from beamformed transmissions in finding the coordinator automatically. The problem is formulated as a K-center problem, which is a NP-hard problem in general. Analysis is carried out to find optimal solutions in certain tractable topologies. Numerical algorithms and simulation results are further presented for random two dimensional topologies.

Low Complexity Adaptive Modulation for 802.11N Beamforming Systems

We study transmit beamforming in IEEE 802.11n systems, where perfect channel state information is available at the transmitter. We first derive the achievable diversity order on each eigenmode. It is found that these eigenmodes are almost Gamma distributed for small number of antennas, which is the typical configuration for IEEE 802.11n systems. Finally, we develop a tight lower- and upper-bound to the average bit error rate performance over each eigenmode.